Subject: Re: [PATCH] revision: use C99 declaration of variable in for() loop

From: "brian m. carlson" <[email-masked]>
Date: Mon, 15 Nov 2021 22:26:32 +0000

On 2021-11-15 at 06:27:45, Junio C Hamano wrote:
> There are certain C99 features that might be nice to use in our code
> base, but we've hesitated to do so in order to avoid breaking
> compatibility with older compilers. But we don't actually know if
> people are even using pre-C99 compilers these days.
> 
> One way to figure that out is to introduce a very small use of a
> feature, and see if anybody complains, and we've done so to probe
> the portability for a few features like "trailing comma in enum
> declaration", "designated initializer for struct", and "designated
> initializer for array".  A few years ago, we tried to use a handy
> 
>     for (int i = 0; i < n; i++)
> 	use(i);
> 
> to introduce a new variable valid only in the loop, but found that
> some compilers we cared about didn't like it back then.  Two years
> is a long-enough time, so let's try it agin.

I think you absolutely need a compiler option for this to work on older
systems.  Many of those compilers support C99 just fine but need an
option to enable it.

I think this could go on top of my patch, though.

> If this patch can survive a few releases without complaint, then we
> can feel more confident that variable declaration in for() loop is
> supported by the compilers our user base use.  And if we do get
> complaints, then we'll have gained some data and we can easily
> revert this patch.
> 
> Signed-off-by: Junio C Hamano <[email-masked]>
> ---
>  revision.c | 4 +---
>  1 file changed, 1 insertion(+), 3 deletions(-)
> 
> diff --git a/revision.c b/revision.c
> index 9dff845bed..44492f2c02 100644
> --- a/revision.c
> +++ b/revision.c
> @@ -43,10 +43,8 @@ static inline int want_ancestry(const struct rev_info *revs);
>  
>  void show_object_with_name(FILE *out, struct object *obj, const char *name)
>  {
> -	const char *p;
> -
>  	fprintf(out, "%s ", oid_to_hex(&obj->oid));
> -	for (p = name; *p && *p != '\n'; p++)
> +	for (const char *p = name; *p && *p != '\n'; p++)
>  		fputc(*p, out);
>  	fputc('\n', out);
>  }
> -- 
> 2.34.0-rc2-165-g9b3c04af29
> 

-- 
brian m. carlson (he/him or they/them)
Toronto, Ontario, CA